Fork me on GitHub
an open source database of all discovered extrasolar planets


The planetary system K2-138 hosts at least 6 planets.

  System parameters
Primary system name K2-138
Alternative system names N/A
Right ascension 23 15 48
Declination -10 50 59
Distance [parsec] 202.6±2.0
Distance [lightyears] 661+7−6
Number of stars in system 1
Number of planets in system 6

ArchitectureArchitecture of the system

This list shows all planetary and stellar components in the system. It gives a quick overview of the hierarchical architecture.

  •  K2-138, stellar object
    •  K2-138 g, planet, semi-major axis: 0.23±0.02 AU
      •  K2-138 b, planet, semi-major axis: 0.034±0.003 AU
        •  K2-138 c, planet, semi-major axis: 0.044±0.004 AU
          •  K2-138 d, planet, semi-major axis: 0.058±0.005 AU
            •  K2-138 e, planet, semi-major axis: 0.079±0.008 AU
              •  K2-138 f, planet, semi-major axis: 0.106±0.011 AU

              PlanetsPlanets in the system

              This table lists all planets in the system K2-138.

                K2-138 g K2-138 b K2-138 c K2-138 d K2-138 e K2-138 f
              Alternative planet names N/A N/A N/A N/A N/A N/A
              Description The K2-138 system is a planetary system that has been discovered by citizen scientists participating in the Exoplanet Explorers project on the Zooniverse platform. The discovery was made with a space based telescope (0.95 m Kepler Telescope). The parameters listed here are those reported by Hardegree-Ullman et al. 2021 and were imported into the Open Exoplanet Catalogue from the NASA Exoplanet Archive.
              Lists Confirmed planets
              Mass [Mjup] N/A N/A N/A N/A N/A N/A
              Mass [Mearth] N/A N/A N/A N/A N/A N/A
              Radius [Rjup] 0.28+0.03−0.02 0.133+0.013−0.012 0.202+0.016−0.015 0.219+0.017−0.016 0.28±0.02 0.244+0.021−0.019
              Radius [Rearth] 3.2±0.3 1.49+0.15−0.13 2.26+0.18−0.17 2.45+0.19−0.18 3.1±0.2 2.7±0.2
              Orbital period [days] 41.966+0.006−0.007 2.3532±0.0004 3.5602±0.0002 5.4048±0.0005 8.2615±0.0005 12.7576±0.0012
              Semi-major axis [AU] 0.23±0.02 0.034±0.003 0.044±0.004 0.058±0.005 0.079±0.008 0.106±0.011
              Eccentricity N/A N/A N/A N/A N/A N/A
              Equilibrium temperature [K] 445+31−30 1157+78−74 1012+65−61 888+57−53 757+52−47 653+45−42
              Discovery method transit
              Discovery year 2021 2017 2017 2017 2017 2017
              Last updated [yy/mm/dd] 21/03/04

              starStars in the system

              This table lists all stars in the system K2-138.

              Alternative star names N/A
              Mass [MSun] 0.92+0.08−0.10
              Radius [RSun] 0.84±0.05
              Age [Gyr] N/A
              Metallicity [Fe/H] 0.13+0.13−0.18
              Temperature [K] 5283+122−163
              Spectral type G8V
              Visual magnitude 12.21±0.03

              Planet sizes

              The following plot shows the approximate sizes of the planets in this system The Solar System planets are shown as a comparison. Note that unless the radius has been determined through a transit observation, this is only an approximation (see Lissauer et al. 2011b).

              PlutoMercuryMarsVenusEarthNeptuneUranusSaturnJupiterK2-138 gK2-138 bK2-138 cK2-138 dK2-138 eK2-138 f

              Habitable zone

              The following plot shows the approximate location of the planets in this system with respect to the habitable zone (green) and the size of the star (red). This is only an estimate, using the star's spectral type and mass. Note that if no green band is shown in the plot, then the planet's orbit is far outside the habitable zone. The equations of Selsis, Kasting et al are used to draw the inner and outer boundaries.

              K2-138 gK2-138 bK2-138 cK2-138 dK2-138 eK2-138 f

              referencesScientific references and contributors

              Links to scientific papers and other data sources


              This table lists all links which are relevant to this particular system. Note that this is just a summary. More references to the scientific publications and comments can be found in the commit messages. To see these, head over the github or click here to directly go to the git blame output of this system. In the left column of the output you can see the commit message corresponding to each parameter. It also lists the date of the last commit and the person making the changes. Within the commit message, you will find a link to the scientific publication where the data is taken from. Note that this is a new feature and not all system parameters might have a reference associated with it yet. Please help making this catalogue better and contribute data or references!

              Open Exoplanet Catalogue contributors

              Contributor E-mail Number of commits
              Andrew Tribick ajtribick(at) 2
              Hanno Rein hanno(at) 4

              This table lists all people who have contributed to the Open Exoplanet Catalogue. Please consider contributing! Click here to find out how. You can also view all commits contributing to this file on github.

              xmlData download

              You can download the xml file corresponding to this planetary system, which is part of the Open Exoplanet Catalogue. All information on this page has been directly generated from this XML file. You can also download the entire catalogue over at github. If you prefer to download the dataset as an ASCII tables, you might find the oec_tables repository useful.


              If you spot an error or if you can contribute additional data to this entry, please send an e-mail to Please include the corrected xml file and a reference to where the new data is coming from, ideally a scientific paper. If you are fluent with git and github, you can also create a pull request or open an issue on the Open Exoplanet Catalogue repository. Please include the reference to the relevant scientific paper in your commit message.